U.S. Pat. No. 4,182,087 to Schall, et al. describes and illustrates an exemplary above-ground, essentially oval swimming pool. Made of multiple panels of extruded aluminum, the pool is designed to be built "without the necessity of a large top and bottom rail and, theoretically, without a top and bottom rail at all." As stated in the Schall, et al. patent, construction of the pool allows use of a lower guide rail "solely for the purpose of shaping" the pool. The guide rail can be removed after pool wall construction is completed or need not be used in the first place in the event that the shape of the outer pool wall has already been marked out.
Because temporary, the guide rail is not subject to forces caused by water as it fills the pool and accordingly has a simple, unslotted "L"-shaped cross section. No base plate, furthermore, is utilized in pools constructed according to the disclosure of the Schall, et al. patent.
U.S. Pat. No. 3,745,593 to Wall, by contrast, details an above-ground swimming pool in which flat base plates and "bottom rail members" are employed. Described therein is the structure of a bottom rail member, which includes a web portion having a pair of spaced apart vertical flanges integrally formed therewith and projecting upwardly therefrom. One of the vertical flanges has an inturned flange integrally formed therewith which terminates in a terminal flange. The other vertical flange projects upwardly beyond the inturned flange.
(Numerals omitted.) Defined between the inner vertical flange and the inturned flange is a slot, in which is received the lower edge of a continuous side wall preferably formed of corrugated sheet metal. No mechanism for guiding the sheet metal appears provided by the bottom rail member, however, and no positive locking means is furnished as part of the rail member itself.
Additionally described in the Wall patent is the structure of a base plate included as a part of a vertical leg support of the completed pool. Intended to be substantially flat, the base plate nonetheless has an upturned inner flange terminating in an inwardly curved upper end. A portion of the inner flange "is also struck inwardly to define a locking element . . . which is adapted to coact with the bottom rails for releasably locking the rails to the base plate." Spaced vertical guide elements of the base plate purportedly define guide ways for pairs of bottom rail members, with the inwardly curved upper end of the inner flange overlying the inner vertical flange of each bottom rail. The "inwardly struck locking element" of the base plate also "serves as a stop to limit inward movement of each pair of bottom rail members which are interconnected with each base plate." Again, however, no positive interlocking mechanism with the bottom rail members is provided, and the base plate lacks any slot for supporting a received upright or vertical leg.